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#1 Scout92

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Posted 02 December 2012 - 12:07 PM

Astronomy supernewby here, and I have a quick question. Is a Meade 4.5 in. f/4 spherical primary from ebay worth the $24 to by it?

#2 kfrederick

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Posted 02 December 2012 - 12:10 PM

A f4 should be parabolic so no

#3 Scout92

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Posted 02 December 2012 - 12:13 PM

whould it be good for anything?

#4 orlyandico

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Posted 02 December 2012 - 12:36 PM

burning ants? :D

those were made for a type of telescope called a "Bird Johnson" where there is a corrector lens in the focuser which (attempts) to correct for the short, spherical primary. This design is only found in the cheapest of telescopes.. and you can guess why.

that said this - http://www.cloudynig...p?product=69629

at $75 is actually worth building a scope around.

but if you really want to build a telescope for cheap, this is a better choice -
http://www.surplussh...item/l3002.html

not quite $25. or this (would result in a shorter telescope but one with more chromatic aberration)
http://www.surplussh...item/l2196.html

#5 Andy Taylor

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Posted 02 December 2012 - 12:36 PM

Carton mirrors

Check these out. Sheldon has loads of good quality stuff and is a great guy to buy from.

PM him to see if he has something suitable. Carton stuff is top quailty.

I'd avoid ebay.

#6 Scout92

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Posted 02 December 2012 - 12:50 PM

Oh man! I was just at that site looking for a 76 mm lens to make a copyscope and didn't see anything like that so I bought a 70mm from eBay! Oh well live and learn thanks for the link. Lol...I might get one there anyway ;) so I ca make 2 scopes, be good practice!

#7 Scout92

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Posted 02 December 2012 - 12:52 PM

Thanks for the tip!

#8 Ksearles62

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Posted 02 December 2012 - 01:55 PM

Don't feel bad. I bought one of the f4 mirrors from ebay for project. Now I have a nice paperweight. Live and learn

#9 dan_h

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Posted 02 December 2012 - 02:01 PM

Carton mirrors

Check these out. Sheldon has loads of good quality stuff and is a great guy to buy from.

PM him to see if he has something suitable. Carton stuff is top quailty.


Sheldon does have some good stuff at reasonable prices. These mirrors don't fall into that category. Our local ATM club just received a number of the 4" f6 mirrors. It is my understanding that they were not top quality. It is a case of you get what you pay for.

dan

#10 Tom and Beth

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Posted 02 December 2012 - 11:42 PM

Astronomy supernewby here, and I have a quick question. Is a Meade 4.5 in. f/4 spherical primary from ebay worth the $24 to by it?


Only if you consider the "mirror" as a blank that is already ground and sorta spherical. If it's been coated you CAN pour a pitch lap and re-figure it.

#11 edsplace

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Posted 03 December 2012 - 08:58 AM

You can find Meade 4.5" F/9 mirrors on eBay. I built a reflector that was carry on luggage for airlines on trips for a trip to Hawaii. The scope worked wonderful!

#12 Ksearles62

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Posted 03 December 2012 - 01:28 PM

Now that I own a set of the 4.5 f4 ebay mirrors, is there anything I can do with them besides burn ants? I already have a different mirror set on the way for a PortaBowl project :smirk:

#13 Pinbout

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Posted 03 December 2012 - 01:33 PM

test their figures, maybe flex it to a parabola

#14 hottr6

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Posted 03 December 2012 - 03:12 PM

Despite all the good suggestion here, please consider if you are going to build or buy a cell for the mirror. New cells for 4" and 4.25" mirrors are non-existent today. Cells for 4.5" are plentiful, both used and new. If you go with the 4" mirror, you will have to build the cell yourself.

The main problem with buying used small mirrors are the coatings; it will cost at least twice as much as the used mirror to have it re-coated by the labs.... if they will even do it.

#15 mikey cee

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Posted 03 December 2012 - 05:21 PM

:foreheadslap:Sheeesh finally someone who knows the difference between "calvary" and "cavalry"! :shocked: It's like screeching chalk on a blackboard to my enlightened ears. :smirk: Mike

#16 kfrederick

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Posted 03 December 2012 - 07:41 PM

Maybe have Ed Turco correct your spherical f4 or Mark Harry

#17 dave brock

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Posted 04 December 2012 - 01:03 AM

Does Mark Harry need correcting? :step:
Sorry, couldn't resist.

Dave

#18 Al8236

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Posted 04 December 2012 - 02:54 AM

:rimshot: Ta da dum!

#19 nytecam

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Posted 04 December 2012 - 05:38 AM

Don't feel bad. I bought one of the f4 mirrors from ebay for project. Now I have a nice paperweight. Live and learn

This is the ATM Forum so you can do better than just burn ants :D Could make a Lensless Schmidt out of one - same mirror in Meade scope here :grin:

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#20 Scout92

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Posted 04 December 2012 - 03:01 PM

Well Mikey I should know I was a scout for 16 years! :D

#21 magic612

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Posted 04 December 2012 - 04:56 PM

Despite all the good suggestion here, please consider if you are going to build or buy a cell for the mirror. New cells for 4" and 4.25" mirrors are non-existent today. Cells for 4.5" are plentiful, both used and new. If you go with the 4" mirror, you will have to build the cell yourself.


Well, an enterprising person could take a 4.5" cell and shim the mirror in the cell so it is centered. ;)

The main problem with buying used small mirrors are the coatings; it will cost at least twice as much as the used mirror to have it re-coated by the labs.... if they will even do it.


All one need do is ask. Check out alcoat.net (I believe he used to coat John Dobson's mirrors). I got a horribly coatings-damaged 4.5" mirror recoated there for about $25 or $30 3 or 4 years ago, IIRC. Coatings were not what I would call perfect, but they looked darn good and it was 95% better than it was beforehand. Views in the scope looked great and I gave the scope to a friend who still happily uses it to this day.

#22 Scout92

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Posted 06 December 2012 - 06:55 AM

About $47 dollars to recoat (35 for the coat 12 for striping) not counting s&h for a 6in at alcoat.net. is that a good price?






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